Extreme weather around the world is unusual this summer
From July 17th to 22nd, there was historically rare rainfall in Henan.
The maximum hourly rainfall in Zhengzhou (201.9 mm) broke through the historical extreme value of hourly rainfall on land in China.
The resulting meteorological disasters have brought heavy losses to people's lives and property, and affected the hearts of the people across the country.
This summer, not only my country, but also the world is showing frequent occurrences of extreme weather and climate.
The areas where these extreme weather occur are mainly concentrated near 40°N latitude.
So what are the leading factors behind these extreme weather events?
Are there any connections between each other?
We specially invited meteorological experts and professional reporters from China Meteorological News to give you an authoritative interpretation.
Why is there so much rainfall in the north this summer
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From July 17 to 22, Henan experienced rare rainfall. The maximum hourly rainfall in Zhengzhou (201.9 mm) broke the historical extreme value of hourly rainfall on China's land. The cumulative rainfall at the Hebi Science and Technology Center Weather Station was 1113.8 mm.
Since July (until 26th), the average rainfall in Hulunbuir, Inner Mongolia, was 38.6% higher than that in the same period of normal years, and the two reservoirs collapsed; the average rainfall in Liaoning Province in June was 170.9 mm, 89.9% more than normal, and it was complete in 1951. The most since meteorological data...
After entering the main flood season in June, heavy rainfall occurred frequently in various parts of the north, and the news that "a certain precipitation process in a certain place exceeded the total amount of precipitation throughout the year" was often reported in the news.
At present, the northern rainy season of "Seven Lower and Eight Upper" (referring to heavy rains in northern China concentrated in late July to early August) has not passed half of the northern rainy season. Such frequent rainfall has brought a lot of pressure on the later flood control.
So, how strong is the rainfall in the north this year compared with normal years?
What is the reason for the strong side?
Which areas will rain frequently in the future?
The northern flood season is earlier than normal
This year, the rainy season in the north came earlier than usual.
According to the monitoring of the National Climate Center, the rainy season in Northeast China began on June 10, 15 days earlier than normal, and the rainy season in North China began on July 12, 6 days earlier than normal.
The early flood season actually reflects more rainfall.
According to Zhao Junhu, the chief engineer and senior engineer of the National Climate Center's flood season forecasting, the rainy areas in northern China this summer mainly appear in North China, Northeast China, Huanghuai and other places.
Monitoring by the National Climate Center shows that since the main flood season this year (from 8:00 on June 1 to 8:00 on July 26), precipitation in North China (Hebei, Beijing, Tianjin, and Shanxi) has been 52.7% more than normal, which is since 1951. The fifth place in history is 13% more in Northeast China (Heilongjiang, Jilin, Liaoning) and 28.3% more in eastern Inner Mongolia.
The Huanghuai area (most of Shandong, northern Jiangsu, northern Anhui, and most of Henan) is 15% higher, of which the average is 67.8% higher in Henan Province and more than 2 times higher in northern Henan.
In the western part of the northwestern region and the northeastern part, and the western part of Inner Mongolia, the precipitation was less than usual, with an average of 32.1% less precipitation.
For the rainy areas in the north, when the overall precipitation is relatively high, the phased heavy rainfall process in some areas has brought heavier rain and floods.
Taking Hulunbuir as an example, the precipitation in Moridawadaur Autonomous Banner from July 1 to 19 reached 271.4 mm, which was 322.1% more than normal in the same period of the year, ranking first in the same period in history.
On the 18th, the open spillway Yong'an Reservoir and Xinfa Reservoir of Moridawadaur Autonomous Banner burst and collapsed, resulting in the flooding of more than 320,000 mu of farmland and the destruction of more than 20 bridges.
Similarly, areas with a lot of previous rainfall should also be highly vigilant about the superimposed effects of subsequent rainfall.
Since the flood season in the north this year has received more rainfall, it is closely related to the active northeast cold vortex and the location of the subtropical high.
According to the difference of the influence system, the precipitation in the northeast flood season can be divided into two stages: early summer and midsummer.
The precipitation anomalies in late spring and early summer (May and June) were mainly affected by the Northeast Cold Vortex and the Sea of Okhotsk blocking high. The precipitation anomalies in July and August were mainly affected by the second northward jump of the Western Pacific Subtropical High.
According to Chen Lijuan, chief forecaster of the National Climate Center, from June 1 to July 10, the northeast cold vortex was active, and the subtropical high in the Northwest Pacific was phased to the north, which is conducive to the convergence of cold and warm air in the northern region.
In Liaoning, the impact of the Northeast Cold Vortex in June (22 days) is 9 days longer than that of normal years. This is the main reason for extreme weather and climate events such as the province's heavy rainfall process, the rainfall exceeding the historical extreme value, and the frequent occurrence of severe convective weather.
After July 6th, the Northwest Pacific subtropical high ridgeline remained stable north of 25°N latitude. After July 15th, the subtropical high ridgeline moved northward to north of 30°N latitude. At the same time, the southwest vortex moved toward North China and Huanghuai. The water vapor conditions Abundant, leading to more precipitation in northern my country.
So, what factors are conducive to the northwestern Pacific subtropical high, the stronger East Asian summer monsoon, and the active northeast cold vortex in early summer, which will lead to earlier floods and more rainfall in the north this year?
Chen Lijuan introduced that this has a greater relationship with external forcing anomalies and influences such as SST and snow cover.
A moderate-intensity La Niña event occurred in the autumn, winter and spring of 2020/2021. This year is the year of attenuation of the La Niña event. The spring and summer sea temperature of the North Atlantic Ocean is distributed in the positive phase of the "-+-" tripole mode from south to north. The snow cover in spring is obviously less, and these external forcing features are all conducive to the factors leading to the above features.
In the middle and high latitudes of North China and Northeast China, the mechanism of the circulation anomaly is more complicated. It is affected by multiple factors such as the underlying surface (the surface of the earth that is in direct contact with the lower atmosphere) and the internal variability of the atmosphere. The reason for the activity of the northeast cold vortex is still Awaits further study.
Affected by global warming, local heavy precipitation increased
The National Climate Center predicts that during the "seven down and eight up" period, my country will have two rainy belts in the north and south. The rainy areas in the north are mainly located in the north and southeast of the northwest, most of Inner Mongolia, northern China, western northeast China, most of Huanghuai, and Jianghan. In most places, the central and eastern parts of Inner Mongolia, most of North China, the northwest of Huanghuai, and parts of the west of Northeast China account for 20% to 50%.
The rainy areas in the south are mainly located in the central and eastern Jiangnan, eastern southern China, and southern southwestern China. The southern and eastern Jiangnan need to pay attention to the impact of wind and rain caused by typhoon activities.
According to the above predictions, the middle and lower reaches of the Yellow River, the Haihe River, Songnen River Basin and parts of the Liaohe River Basin, the lower reaches of the Yangtze River, and the Pearl River need to guard against periodic storms, floods, and heavy floods.
Experts also reminded that due to the impact of global warming, the frequency and intensity of local heavy precipitation have increased, and the extremes have become stronger, so corresponding prevention work and preparations must be made.
(Li Yipeng Chen Keyao)
Why is this heavy rain in Henan so fierce?
Heavy rain is the product of the interaction between various weather and circulation systems, especially extreme heavy rain or continuous heavy rain, which appear in several time-scale weather systems (planetary scale, weather scale, mesoscale and small scale), and there is obvious interaction. Case.
In terms of the heavy rain in Henan that began on July 17-
The planetary-scale subtropical high and continental high were maintained in the Sea of Japan and the northwestern region of my country, respectively. The low-value weather system of the weather scale was "sandwiched" between the two and could not move, causing heavy precipitation in central and western Henan for a long time;
The situation on the ocean surface is also unrest. Typhoon "Fireworks" was generated and approached our country, and a large amount of water vapor was transported to the inland areas;
In addition to the terrain "assist", that is, the special terrain of the Taihang Mountains and Funiu Mountains has a convergence and uplifting effect on the easterly airflow, and the precipitation in front of the windward slope has increased significantly;
Under the large-scale background that is conducive to the occurrence of heavy rains, the small and medium-scale convective systems are also "restless".
It repeatedly develops in the piedmont area of Funiu Mountain and moves towards Zhengzhou, resulting in high rainfall intensity and long maintenance time, causing local extreme heavy rainfall and so on.
It can be said that no time-scale weather system is "innocent" when there is a heavy rainstorm.
Under the interaction of planetary scale, weather scale, and small and medium-scale weather systems, coupled with the "assistance" of special terrain, a rare rainstorm that broke the historical extreme value finally landed in Henan.
(Wang Meijue)
Four main characteristics of summer rainstorm in my country
my country is a country with heavy rains. One of the main reasons is that it is deeply affected by the East Asian summer monsoon every summer.
The occurrence and prevalence of summer storms coincide with the rainy season or flood season in our country, which is the season with heavy rains.
The monsoon air current brings abundant water vapor and unstable air from the sea, which is one of the key reasons for the occurrence of heavy rains.
With the onset, prevalence of summer storms and the rapid or slow advancement of the north, my country's main rain belt is also moving north, affecting South China, Jianghuai, and North China successively.
The heavy rain in my country has four main characteristics-
Time is concentrated.
Heavy rains in my country mainly occur during the flood season from May to August, and the peak period is concentrated in late June to early July. This is the famous East Asian rainy season.
The torrential rains in North China were concentrated from late July to early August, that is, "seven down and eight up".
High intensity and high extreme value.
Compared with other countries in the same climate zone, the extreme value of heavy rain in my country is very high.
For example, during the heavy rainfall on July 20, a single station near Zhengzhou has exceeded 200 mm/h, breaking the record set by Henan Linzhuang on August 5, 1975; another example is September 10, 1963, with 24-hour precipitation. The extreme value appeared in Taiwan, reaching 1248 mm, breaking the world record.
The duration is long.
Statistics show that the duration of heavy rains in my country ranges from a few hours to 63 days.
Some studies even believe that the Meiyu in 1986 lasted 65 days.
The scope of influence is large.
The area of heavy rain in the Yangtze River Basin is the largest in the country, and the rain belts are mostly east-west. For example, heavy rains in 1954 and 1998, precipitation areas of more than 600 mm covered most of the Yangtze River Basin; heavy rains in the Jianghuai River Basin in 1991 The area also covers hundreds of thousands of square kilometers.
Based on the above factors, heavy rain can cause large-scale floods, especially continuous heavy rain, which is one of the main meteorological disasters affecting our country.
Affected by heavy rain, there are mainly 5 areas in my country that are vulnerable to floods, and their occurrence frequency varies.
1 to 2 times every 3 years in southern China, 2 to 3 times a year in Hunan and northwestern Jiangxi, once every 2 to 3 years in the middle and lower reaches of the Yangtze River and east China coast, once every 2 to 3 years in Huaihe and Yellow River basins, Songhua in eastern Northeast In the Jiang and Liaohe river basins, every 7 to 8 years.
(Zhang Yibo)
The downpour in the north is actually no less than in the south
The vast northern area of China usually appears as the opposite of "Amidst the Rain and the South of the Yangtze River".
In the middle school geography textbook, China's annual precipitation is condensed into a concise distribution map. The curves of different colors above outline the picture of "more rain in the south and less rain in the north".
However, in mid-to-late July to mid-August in mid-summer every year, northern my country will enter a rainy period.
In a few days or even a few hours, sometimes it will rain enough for half a year in parts of the north.
If we have a lens focusing on time, we can clearly see an atlas related to heavy rain——
The focus is adjusted to 24 hours. If the north and south are divided by 30° north latitude, the number of stations where extreme precipitation occurs for 24 hours, the number of stations in the south and the north is about 7 to 3.
By 6 hours, 3 hours, and 1 hour, this gap was quickly narrowed, and the number of corresponding extreme precipitation stations to the south and north was basically tied.
Among them, the coordinates are in Hebei, Henan, and Shandong in the north, as do Guangdong, Guangxi, and Hainan in southern China, with surprising front row data.
By projecting the individual experience, it becomes clear: the terrible downpour is actually no less in the north than in the south.
The blessings of high rainfall intensity and short duration have made many extreme records of heavy rainfall in China originate from North China and Northeast China.
Unlike the Meiyu in the Yangtze River Basin, the topography also affects the heavy rains in North China and Northeast China.
The windward side and mountainous areas of many northern mountains are often catalysts for heavy rains.
(Lu Jian, Zhao Xiaoni, Li Hui)
Disaster prevention knowledge
Lightning, Windproof and Waterproof Scientific Response to Strong Convective Weather in Summer
Most of the memories of summer have sudden rainstorms, which caught people off guard.
Weather with short duration, violent performance, and strong destructiveness like heavy rain is severe convective weather.
As the name implies, severe convective weather is a severe weather process caused by strong convection, mainly including short-term heavy precipitation, hail, tornado and torrential currents, and its destructiveness is second only to tropical cyclones, earthquakes, and floods.
Researcher Sun Jisong of the Chinese Academy of Meteorological Sciences reminded that if you are accidentally exposed to strong convective weather, you must pay attention to three aspects of disasters:
Lightning protection.
Strong convective weather is often accompanied by thunder and lightning.
If you are in the wild, avoid sheltering under trees from rain. Tall trees often act as a lightning source. Avoiding rain under trees will inevitably be implicated and injured by lightning strikes. Don’t stand in open areas to avoid “thundering” on your upper body.
It is not advisable to carry badminton rackets, fishing rods, bamboo poles, etc. on your shoulders when encountering lightning and thunder.
Windproof.
The damage of the wind itself cannot be compared with other disasters, but there are rare cases of casualties caused by wind disasters every year.
Experts reminded that when encountering windy weather, you must not take shelter for a while and take refuge near billboards, dangerous walls, etc.
The safest way is to choose shelter in a frame structure building with better windproof effect.
water proof.
In heavy rain, keep people and cars away from the water body, and don't wade easily.
Due to ground runoff effects, low-lying places can rise quickly, and can even reach a speed of several meters within a minute, which can easily cause the car to stall or even be flooded.
When the car is turned off in a low-lying place, do not wait in the car, get out of the car and wait for rescue at a high place.
Pedestrians should not wading rashly.
In order to quickly drain water during heavy rains, many manhole covers will be opened.
When you see a vortex, take a detour to avoid falling into the manhole, pit, or hole, which may cause injury.
(Zhang Yibo)
global vision
Extreme weather and climate such as high temperature, heat waves, floods, droughts, etc. frequently occur-
Who touched the extreme weather switch in the northern hemisphere
Recently, extreme weather and climate have occurred frequently in the world, and floods have been raging in parts of Europe; the United States and Canada have experienced continuous high temperature weather and droughts have become increasingly serious; Japan has been attacked by "violent plums"; extreme rainstorms have occurred frequently in the Huanghuai area of North China... The occurrence areas are linked together and it can be found that they are mainly concentrated near 40°N latitude.
So who shakes the belt of 40°N latitude and turns on the switch of extreme weather in nearby countries?
Is there a butterfly effect-like association between these extreme weather events?
Should climate warming be the leading factor behind it?
In fact, it is not just the recent weather anomalies, but the overall global climate anomalies from January to July 2021 are significant, especially in the mid-to-high latitudes of the northern hemisphere.
In winter, the extreme winter storm "Uri" appeared in North America, Texas suffered a once-in-a-century blizzard and a century-old drought in California and other places on the west coast of the United States in the spring. The high summer heat waves in the region set historical records and further aggravated the development of drought.
Recently, the east coast of the west coast of the United States has shown a combination of wet and dry sky, and the "deep water" in the east is "hot" in the west.
Our country has also experienced a variety of extreme weather. There was an extreme cold wave to cool down in the previous winter, and the dust storm in spring was unusually active. The national average temperature in the first half of the year was 8.7°C, 1.2°C higher than the same period in normal years, the highest in the same period since complete meteorological records... …
This series of extreme weather events were not caused by the butterfly effect. Rather, under the background of global warming, the meridian of the mid-to-high latitude circulation system increased, and blocked high pressures appeared in North America and other places, thus forming deep upstream and downstream. The large trough of the U.S. thus presents a situation of "dry and wet weather" on the east coast of the west coast of the United States. The situation in Europe is also related to the control of the deep low-value system on the west side of the Ural Mountains blocking the high pressure.
The high-altitude jet axis in the westerly zone is undoubtedly the main driver of the chain reaction of the abnormal atmospheric circulation near 40°N latitude.
The biggest difference between my country's main flood season rainfall belt and previous years is the appearance of southwest-northeast trend. The key factor is the shape and location of the western Pacific subtropical high.
In addition, the factors of climate change cannot be ignored.
Global warming has led to an intensified water cycle in the climate system, increased local water vapor convergence, increased tropospheric water vapor conversion, increased precipitation intensity, and increased precipitation extremes.
Generally, two important facts of global climate change are global warming and frequent occurrence of extreme weather and climate events.
(Li Hui Wu Peng)